In the past 3 years K. Ozato has studied the degree of unusually extensive polymorphism and molecular heterogeneity of mouse H-2 antigens by developing monoclonal antibodies. Recent recombinant DNa technology allowed us to isolate several H-2 like genes from BALB/c genome directly. The trnsfer of such isolated genes into mouse L-cells has been achieved. We detected expression of the transferred genes by testing the reactivity of monoclonal antibodies of defined specificity. The assignment by the antibodies agreed with DNA sequence results. Thus we identified 2 genes to be h-2 Ld and Dd. The new genes have been evaluated for various immunological parameters, such as ability to elicit antibody response, recognition by allloreactive or hapten (virus) specific H-2 restricted T cells. These studies provided the foundation for the next step for determining precise DNA sequence responsible for the immunological parameters described above.